Range finder with light beam correction



April 3, 1951 M. SCHWARTZ ETAL RANGE FINDER WITH LIGHT BEAM CORRECTION Filed Feb. 28, 1946 TORNEY Patented Apr. 3, 1951 res :-Inc., Stamford, Conn.

Application February 28, 1946,Serial NoJ65m927 '7 Claims.

This invention relates to light beam projecting range finders, particularlyto rangefinders o'f'the type in which a source oflight-is positioned be tween two light deviating -means or reflectors, one of which is-movable, and in which the-angular position of the movable reflector relative :to the stationary one is employed, either to ascertain the range of an object or to focus the lens of a photographic camera, the latter 'type of range finders being sometimes-referred to lens coupled range finde'rsl Theword camera, as used lherein, isintended to include apparatus for the taking of photographs as well as .devices, such :as moving picture projectors, ltelevision c'amera's, enlargers, :and the iikeyor in other words, any device icomprisinga lens to be focused on an-object-or screen.

In range *findersof the type above referred to, the source of light usually comprises an electric lamp having an'incandescent filament, two images of which areyiewable on the object. The relative position of :these images -is varied "by means of the movable reflector, and the "two images are brought into a predetermined position relative to each other which is indicativeeof the range of the object.

,As will be evident to a person skilled {in the art, the accuracy of a range finder of the type above referred to will be affected :by a variation of the position of the lamp filament relative to the two reflectors because any variation of the filament position will cause the images to be viewable on the object in "a different relative position fora given range of the object. It shas been found that in electric lamps, as commercially available-on the market, the filament is not always in the same position. Furthermore, the lamp will not always be inserted in the socket in the same position. As aresult, when a new lamp isinser-ted, it may be found that the filament of such ,new lamp is changed relative to a plane parallel to an axis between the two reflectors, and/or that the filament of the new lamp is slightly tilted relative to 'a plane through the filament-of the old lamp. Either suchchange of the filament position :will result in altered light paths.

, An arrangement for correction of a tilting of the lamp has been fully described and disclosed in the co-pending application, Ser. No. 648,726, vfiled February 19, 1946, by Morris Schwartz and William Castedello, which application is now abandoned. The main object of this invention is to :provide :means by which any inaccuracy caused by a 2 change :of the filament position relative to a plane'through-or parallel to -=an a-xis between the two reflectors is automatically corrected.

Another objectof theinv'entioh is to provide means which correct a variation "of the light pathsas cause'd by a change of -the filament posi tion relative to a plane through "or parallel to an axis between the refl'ectors Without "requiring an adjustment -of any component parts of the range finder.

Another object of the invention is "to provide optical means which maintain the two :be'ams projected by :the range finder "always parallel to each other for all adjustmentsxof the range finder requiring such paralle'lismof the light 'beamsimdependently .of a variation of the filament :pOSl': tion relative tothe refiectors. I

.Other and further obje'cts, features and advantages of the invention -will vbeset :iorth hereinafter and the novel :fea'tures thereof idefineli by the appended claims.

The :present application is ;a continuation in part of the copending application Ser. -'-,N,o. 494,87 2, fi'led'on July "15,1943, by Morris schwartz and William Castedello and "issued :as Letters Patent $403,308 enema .1946.

In the accompanyin drawin s severa n w preferred embodiments are shown :by way 915 illustration and not by way rof limitation.

-. .Fig. :1 :is cal-di rammatic view of the optica components of a light beam proj cting rane finder according to the invention.

Fig.f2=is-a planiview of a light beam projecting rangefinder including an electric lamp accord ing to the invention.

Fig. 3 ;is a diagramma ic :view of the optical components of 1a modification of a light beam projecting range finder according to the i-ihVQHF tion, and

Figs. 4 :and 15 are diagrammatic @views of the images produced :by a light ibeam projecting range finder according to the invention 011.131!

object, the images being shown in different positions of adjustment.

Referring now to "the natives in detail, the o tical system of the flight "beam projecting range finder, as shown in Fig. '1, com'prises an electric damp til havinga filament :H. This lamp directs a beam of light toward a Lpivotai zligh-t. :de'viating means l2 such as Ia fully silvered mirror or a prism which :re-directs the beam of light :tow'ard an-object the rangeof which is to be ascertained.

Ihetbeam-lof lightr'eflected by mirror .12 :iszpassed "through an image forming ilens .213 .so that an image of filament ill zvicwable on the object.

3 A second beam of light from lamp I is passed through a second image forming lens I4 toward a second stationary light deviating means I which redirects a second beam of light toward the object so that a second image of filament II is viewable on the object. According to the invention, light deviating means I5 is a means having constant 90 deviation characteristics and is shown in Fig. 1 as a pentaprism.

As it will be apparent to any person skilled in the art, the relative angle of the light beams projected toward the object and hence the relative position of the two images, as viewable on the object, will be controlled solely by the angular position of mirror I2, assuming the position of filament I I relative to the optical components of the range finder remains unchanged.

Various arrangements are well known in the art in which the angular position of the pivotal mirror is used, either to measure the range of an object or to focus the lens of a camera, the correct range of the object being indicated or the lens being focused when the two images viewable on the object are in a predetermined position relative to each other, for instance coincide in the plane of the object.

Fig. 2 shows diagrammatically the essential parts of a lens coupled range finder. A range finder according to Fig. 2 is mounted on a base plate 20 which may be attached to the camera or disposed within the camera casing. Lamp I0 is supported on base plate 20 by means of a holder or'mounting generally designated 2|. Holder 2| permits an adjustment of lamp Ill and hence of filament II relative to a plane vertical to the optical axis between the center of mirror I2 and prism I5 and also in direction of the longitudinal axis through lamp II]. Current is supplied to the lamp by means of a connector generally designated 22, also mounted on base plate 20. Holder 2| and connector 22 are fully described and illustrated in the co-pending application Ser. No. 648,726 filed on February 19, 1946, by Morris Schwartz and William Castedello.

Pentaprism I5 is stationarily fastened to base plate 20 by any suitable means such as a bracket (notshown) Lens I4 associated with pentaprism I5 is supported by a bracket '23 which is slidably mounted on base plate 20 by an elongated slot 24 and a set screw 25 to permit an adjustment of the lens position relative to lamp filament I I and pentaprism I5. The pivotal mirror I2 is backed by a frame 26 which is pivotally supported on base plate 20 by means of ears 21 and a pivot 28 rotatable in a bearing 29. Frame 26 has an extension 30 which serves to support lens I3. This lens is fastened to an arm 3I slidably mounted on extension 30 by a set screw 32 and an elongated slot 33 to permit an adjustment of lens I3 relative to mirror I2. The distance between the lenses and filament II should be selected so that The angular position of mirror I2 is controlled by a rocking movement of a shaft 35 which in turn may be controlled by the adjustment of the lens support of a camera. However, it should be noted that the invention shall not be limited to the illustrated adjustment of mirror I2.

Shaft 35 carries a lever 36 which is fastened at one end to the shaft by any suitable means. A second lever 31 is pivoted at one endto the other end of lever 36. The other end of lever 31 is pivoted to a third lever 38 which in turn is pivoted to a guiding bar or compensator 39.

Compensator 39 has a wedged portion 40 and engages a pin or projection 4| of a lever or bar 42 fastened to or integral with frame 26 supporting mirror I2. The upper edge of compensator 39 is guided by a lug 43 fastened to base plate 20. A loaded spring 44 supported on base plate 20 urges compensator 39 into engagement with lug 43 and a second loaded spring 45 urges wedged portion 40 of compensator 39 into engagement with pin 4I.

As will be apparent, a rocking movement of shaft 35 in either direction will be transmitted to lever 42 and cause a corresponding pivotal movement of mirror I 2.

In light beam projecting range finders of the type, asherein referred to, the light deviating means I2 and I5 are always so constructed and adjusted that the'two light beams projected by the range finder are parallel to each other when the pivotal light deviating means (mirror I2) is in an angular position corresponding to the maximum measuring range of the range finder and beyond such range, Whereas the two light beams are at an angle to each other when mirror I2 is turned for range finding within the measuring range of the range finder. As was previously explained, range finding is accomplished by moving mirror I2 into an angular position in which the two images viewable on the object appear in a predetermined position relative to each other. Consequently, the angular position of mirror I2 for a given distance between the range finder and the object must be a fixed one in order to attain accurate indications. Such fixed angular position of mirror I2 for a given range presupposes that the two light beams are always parallel when the range finder is adjusted for maximum measuring range. In case of lens coupled range finders, mirror I2 is usually so adjusted that the two light beams are parallel to each other when the lens is in its, infinity position. As previously mentioned, the adjustment of the optical components of the range finder requires a definite and unchanged position of fila ment II relative to mirror I2 and prism I5. Any variation of the position of filament II will result in an alteration of the light pathswhich in turn will upset the adjustment of the range finder causing inaccurate indications. As previously mentioned, in electric lamps, as commercially available, the filament is not always in the same position. When the lamp which was inserted in the range finder at the time the range finder was adjusted is replaced by a new one, it will be frequently found that the filament of the new lamp is in a position different from the file.- ment of the old lamp, either due to a variation in the manufacture of the filament or due to the fact that the lamp is inserted into the socket in a manner somewhat different from the manner in which the old lamp was inserted. Variations in the filament position resulting in a displacement of the filament toward the left or toward the right (as seen in Fig. 1) can be compensated for by the adjustable lamp holder as fully disclosed in the aforementioned pending application. The main purpose of the present applica tion is to compensate for alterations of the light paths caused by a displacement of the filament in axial direction, that is by a higher or lower position of the filament (as seen in Fig. 1). 'It should of course be understood that terms high-'- er or lower are correct only when applied to position of the optical components, as shown in Fig. land are used herein merely to define a variation of the filament position relative to a asst plane parallel to the opticalaxi'sbetween mirror I2 and pentaprism I5.

in ordereto facilitate the understanding of the inventiongitbe first assumed that-pentaprism I beireplaced by a reflector suchzas mirror I2. It willthenbe evident to a personskilled in the :art that a variation of the filament position jnaxial direction, .say a-higher ;.po sition .of filament .H, will result in two light beams that are no longer parallel to each other when mirror I2 is placed in a position corresponding to the maximum measuring range of the range finder, thereby causing faulty indications throughout the entire measuring range of the range finder. Let it be now assumed that filament I I be in a higher position in a rangefinder according to the invention in which light deviating means I5 consists of a means having constant 90 deviation characteristics. As a result of a higher position of filament II which is indicated in Fig. l by dashed lines, the light beam (shown in dashed lines), as reflected by mirror I2 will constitute an angle (a) with the light beam (shown in dashed-dotted lines), as reflected by mirror I2 when filament I I is in its original position, (shown in full lines). The second light beam will also be reflected by prism I5 at an angle to the light beam as reflected by the pentaprism when filament II is in its original position. Due to the constant 90 deviation characteristics of prism I5, this angle will be alwaysthe same angle (a) as the angle between the light beams reflected by mirror I2. Consequently, parallelism between the light beams as projected by the light deviating means will be maintained in any higher position of filament II. The same is true when the filament II is in any lower position, the only difference being that then the dotted light beams will be at the opposite side of the dashed-dotted light beams.

It will of course be understood that the corrective properties of pentaprism I5 are limited by the size of the pentaprism, but experience shows that variations in the filament position are rarely if ever beyond the corrective range of pentaprism I5.

Fig. 3 shows a modification in which pentaprism I5 is replaced by two stationary fully silvered mirrors I5 and I5" arranged at a relatively acute angle to each other. These mirrors correspond to the reflecting surfaces of penta prism I5 and hence constitute a light deviating means having constant 90 deviation characteristics. As a result, mirror I5 and I5 will always maintain parallelism between the reflected beams independently of a variation of the filament posi-.- tion, as previously described.

It should be understood that the invention is not and shall not be limited to the light deviating means, as herein disclosed but that other light deviating means may be provided having constant 90 deviation characteristics.

Fig. 4 shows an object 50 on which two images I I and II of filament II are viewable. These images are shown separated from each other, thereby indicating that the angle of mirror I2 does not correspond to the correct range of the object.

Fig. 5 shows the two images in a super-imposed position, thereby indicating correct adjustment of the angular position of mirror I2 which in turn will result in a correct focusing of the camera lens in case of a lens coupled range finder, as has been explained in connection with Fig. 2.

What is claimed as new and desired to be secured by Letters Patent is:

1. A light beam projecting range finder comreceiving light from said :lightrsourceand directs ing abeam-of light towardan object, and a second light :deviating mean-s "receiving light from said light source and directing a second beam of light toward the object, said "light deviating means being constructed -.to be movable relative :to each other for varying the angular relationship of said light beams, one of the light deviating means having constant deviation characteristics.

2. A light beam projecting range finder comprising a light source, a first image forming lens means receiving light from said light source, a first light deviating means receiving light from said first lens means and directing a beam of light toward an object, a second light deviating means receiving light from said light source, and a second image forming lens receiving light from said second light deviating means and directing a second beam of light toward said object, said light deviating means being constructed to be movable relative to each other for varying the angular relationship between said light beams, one of the light deviating means having constant 90 deviation characteristics.

3. A light beam projecting range finder comprising a light source, a first image forming lens means receiving light from said light source, a first light deviating means receiving light from said first lens means and directing a beam of light toward an object, a second light deviating means receiving light from said light source, and a second image forming lens receiving light from said second light deviating means and directing a second beam of light toward said object, one of said light deviating means being pivotal for varying the angular relationship between said light beams, the other light deviating means having constant 90 deviation characteristics.

4. A light beam projecting range finder as described in claim 2, wherein the light deviating means having constant 90 deviation characteristics comprises a pentaprism.

5. A light beam projecting range finder as described in claim 2, wherein the light deviating means having 90 deviation characteristics comprises a pair of mirrors mounted at a relatively acute angle to each other.

6. In a. light beam projecting range finder including a light source, in combination a pair of images forming lenses and reflecting means for directing a pair of images of the light source on an object whose range is to be determined, one of said reflecting means being a movable mirror to eflect coincidence of the images on the said object, the other reflecting means comprising a constant'90" deviation prism, whereby a slight displacement of the light source relative to the optical axis of the range finder will result in displacement of the images which are equal and in the same direction.

7. In a light beam projecting range finder, in combination an exchangeably mounted electric incandescent lamp having a filament, an image forming lens and a reflecting means mounted on either side of the lamp in an optical relationship with the lamp filament for directing a pair of images of the filament to an object whose range is to be determined, one of said reflecting means being a movable reflector to effect coincidence of the images on the said object, the other reflecting means having constant 90 deviation characteristics, whereby a slight displacement of the filament position relative to the optical axis between the reflecting means will result in displacements of the said images that are equal and in the same direction.

. MORRIS SCHWARTZ.

WILLIAM CASTEDELLO.

REFERENCES CITED The following references are of record in the file of this patent:

8 UNITED STATES PATENTS Number Datei:

Name Konig et a1 June 2, 1908 Konig -Q May 20, 1913 Kohler Apr. 8, 1924 Fischer -Liluly 3, 1945 Mihalyi June 4, 1946 Schwartz et a1 July 2,1946 

